In various mechanisms for transmitting a rotational torque, the end portions of two rotating shafts are coupled to each other by means of a coupling. For example, the output rotating shaft of a motor and the input rotating shaft of a pump are connected by means of the coupling. In this case, it takes a considerable amount of labor to carefully install the motor and the pump so that the output rotating shaft of the motor and the input rotating shaft of the pump fully align with each other. Further, even if the installation is carried out by paying ample attention to such an alignment, some eccentricity and angular deviation remain between both rotating shafts, and further vibrations take place to the motor or the pump when they are actuated. In order to absorb these by the coupling portion, a flexible coupling using a flexible member such as a spring or rubber has conventionally been used. In addition, an Oldham coupling has been used as one which can cope with the eccentricity or angular deviation.
With such a shaft coupling, in general, a proper mount member is each mounted to the end portions of the driving shaft and the driven shaft respectively to couple the mount members at the side of the driving shaft and the driven shaft respectively by means of a proper mechanism.